Aminoglycoside antibiotics are essential for battling life-threatening bacterial infections. Aminoglycosides also cause permanent deafness/balance disorders and nephrotoxicity in more than 120,000 individuals each year in the US, particularly in infants and premature babies. The long-term goal of this research is to prevent cochlear uptake of aminoglycosides and thus ototoxicity, hence preserving auditory function. Significant progress in this research has revealed that the cytoplasmic uptake of aminoglycosides can be blocked in sensory hair cells in vitro. In this proposal we seek to block the intra-cochlear uptake and transport of aminoglycosides from the vasculature into the cochlear fluids and tissues in vivo, and prevent aminoglycoside-induced inner ear sensory hair cell death. Our working hypothesis is that: pharmacological agents can reduce aminoglycoside uptake and toxicity in the cochlea. The specific aims of this project are to: Aim 1: Regulate aminoglycoside uptake in vitro, by identifying how pharmacological agents change the intracellular milieu of model cell lines and hair cell explants to inhibit aminoglycoside uptake. We will monitor the calcium concentrations, pH levels, resting potential and membrane resistance. Aim 2: Preserve auditory function and morphology in vivo using inhibitors of aminoglycoside uptake. We will assess the efficacy of these aminoglycoside-uptake inhibitors using auditory brainstem response audiometry, confocal microscopy of hair cell morphology, and constructing cytocochleograms. Aim 3: Identify the intra-cochlear route of aminoglycosides from the vasculature to the sensory hair cells. We will use cochlear perfusion techniques, and sample cochlear fluids to determine if aminoglycosides take an endolymph or perilymph route to enter hair cells. We will then verify that aminoglycoside uptake-inhibitors reduce the intra-coch lear transport of aminoglycosides by one or both routes. Identification of mechanisms that reduce aminoglycoside transport into, and within, the cochlea will determine if currently-available Pharmaceuticals can preserve auditory function during life-saving aminoglycoside therapy of bacterial infections. This may lead to new co-therapeutic treatments with aminoglycosides and (cellular) aminoglycoside-uptake inhibitors against a wider range of bacterial infections.